Trucks and other vehicles are weighed on public weigh scales for commercial purposes including transactions based on weight and to compare actual weights to state limits of weight or to obtain overweight permits. Most states charge and collect significant fines from truck drivers for overweight penalties to prevent harm and promote safety issues related to its roads and bridges.
While the maximum allowed weight varies, the common standard is 80,000 pounds gross vehicle weight. Weight is usually calculated in two measurements: (1) axle weight, the amount of weight carried by each axle and (2) the gross weight, the combined weight of all the axles. To inspect the weight of a truck and its load, weigh stations are equipped with truck scales. There are a variety of scales employed from single axle scales to multi-axle sets. Various systems may be used in truck scales, including, for example, load-cell systems, a bending-plate system, and piezo-electric systems.
In addition to the different types of scales used, there are at least three methods of obtaining the weight of a truck, including a “one-axle” method in which a truck gradually drives across a single scale, stopping each time a set of axles are on the scale. Once the desired axles have been weighed, the total weight of the axle groups are added together to calculate the gross weight. Another method is the “one-stop” method in which a series of scales are used such that the entire truck is weighed at once using multiple platforms placed in a configuration which will place desired axle groups on the individual platforms.
Once weighed, signal lights are often used to indicate if the driver should move the truck from the scales to an inspection area for additional inspection (in the event the truck is determined to be overweight) or if the truck may return to the highway. If a truck weighed at a weigh station is found to exceed the allowable maximum weight, the driver of the truck may receive an overweight ticket and may or may not be required to offload the extra freight. In some states an overweight truck may not be allowed to exit the weigh station until the truck comes into compliance with weight restrictions. Offloading the extra freight may not be practical for items such as, but not limited to, perishable or hazardous loads.
The penalties for a vehicle not falling within the weight guidelines that each state has in place for its road system are often severe. Therefore, a weighing service has been developed which permits a driver the ability to pre-weigh their load prior to encountering a state monitoring site. The weighing services, which may be a certified (i.e., “legal-for-trade”) or a compliance weighing, are typically at truck stops which weigh the trucks. If the weighing service indicates that the truck and trailer are overweight, the driver may respond by removing cargo from the trailer and/or readjusting the weight on the trailer bed. The weighing service verifies the weight of the vehicle and issues a receipt of weight to the driver. Although states may not unconditionally recognize these weigh receipts, should the driver be in violation of a state's weight guidelines, the CAT Scale Company may pay the overweight fine or send a representative to appear in court with the driver as an expert witness if the weight shown on the CAT Scale™ weigh receipt indicates that the vehicle is within the legal weight limits.
Because many shippers do not have scales at their facility, truck drivers may not be able to weigh their vehicle and/or verify that the load is properly distributed among the axles prior to reaching a weigh station. As a convenience to truckers, truck scales, such as CAT Scales are available at many truck stops, or remotely attended locations. This allows the driver to weigh the vehicle and/or verify proper load distribution prior to being weighed at a weigh station or passing an electronic weigh station bypass, or in order to obtain permits for overweight vehicles. These scales will give the driver a reading of each axle and/or the gross weight of the axles. In the event one axle is over the maximum allowable weight, weight may be shifted by sliding the fifth wheel or sliding the trailer tandems to adjust the weight distribution among the axles or in the case of a vehicle with fixed axles, the load may be redistributed to obtain weight limit compliance.